Multi-motor switching system and method for optimized performance

Abstract

A multi-motor switching system and method for obtaining a global optimization of performance criteria that takes into account variables and conditions across an entire driving cycle. The controller of the system is adapted to conduct a global optimization in that it determines the most optimal distribution of motor loads over an entire trip or driving cycle, as opposed to sequentially determining the optimized solution for a given point of time and localized set of current condition. In one embodiment where the control system provides for global optimization, the controller receives trip information through a trip planning tool. The controller utilizes the trip information to generate a driving cycle and further incorporates this information into the optimization process performed by the controller to determine the optimal solution for the entire trip.

We claim: 
     
       1. A multi-motor system capable of performing a global optimization in order to determine an optimal contribution of torque from motors in a vehicle based on a given torque demand in order to achieve a performance objective over an entire driving cycle while remaining within one or more constraints, the system comprising:
 a plurality of motors mechanically coupled to a shaft, wherein the plurality of motors are electric motors; 
 a database that stores efficiency data associated with each of the plurality of motors, wherein the efficiency data represents the efficiency of a motor across combinations of speed and torque; 
 a controller for receiving driving cycle information for a driving cycle, and for generating torque commands for the plurality of motors; 
 wherein the controller generates torque commands for the plurality of motors by performing an optimization analysis across all time periods in the driving cycle with respect to potential combinations of torque contributions by the motors, the optimization analysis comprising:
 determining based on the driving cycle information a required shaft speed and torque across all time periods in the driving cycle; 
 calculating, based on the efficiency data, a cost function for the performance objective across all time periods in the driving cycle for each of the potential combinations of torque contributions by the plurality of motors; 
 identifying from the potential combinations of torque contributions one or more combinations of torque contributions that meet the performance objective based on the cost function and that remains within the one or more constraints; and 
 generating, for each time period in the driving cycle, torque command signals for each of the plurality of motors in order to cause the plurality of motors to drive the shaft according to the one or more combinations of torque contributions to meet the performance objective while remaining within the one or more constraints. 
 
 
     
     
       2. The system of  claim 1  wherein the performance objective is meeting a target efficiency value and where the cost function for each of the potential combinations of torque contributions by the motors is the amount of energy used. 
     
     
       3. The system of  claim 2  wherein the controller estimates for each time period in the driving cycle the energy consumed, and wherein the controller outputs an estimated total energy consumption for the driving cycle. 
     
     
       4. The system of  claim 2  wherein the optimization analysis performed by the controller further comprises integrating an optimization of energy regeneration from braking. 
     
     
       5. The system of  claim 1  wherein the one or more constraints includes the temperature for each motor. 
     
     
       6. The system of  claim 1  wherein the optimization analysis performed by the controller further comprises, for each time period in the driving cycle, calculating the efficiency of each motor in the plurality of motors at the next period in the driving cycle based on the efficiency data and one or more transients. 
     
     
       7. The system of  claim 6  wherein the one or more transients includes thermal transients, and wherein the optimization analysis performed by the controller further comprises calculating thermal transients to determine an estimated temperature for each of the plurality of motors at the end of the next time period. 
     
     
       8. The system of  claim 1  wherein the system is housed within an electric vehicle. 
     
     
       9. The system of  claim 1  wherein the system further comprises a trip planning tool, and wherein the trip planning tool generates the driving cycle information. 
     
     
       10. The system of  claim 1  wherein the performance objective is maximizing driving range. 
     
     
       11. A method of performing a global optimization in order to determine an optimal contribution of torque from motors in a vehicle based on a given torque demand in order to achieve a performance objective over an entire driving cycle while remaining within one or more constraints, the method comprising:
 storing efficiency data associated with each of the plurality of motors coupled to a shaft, wherein the plurality of motors are electric motors, and wherein the efficiency data represents the efficiency of a motor across combinations of speed and torque; 
 receiving driving cycle information for a driving cycle; 
 generating torque commands for the plurality of motors by performing an optimization analysis across all time periods in the driving cycle with respect to potential combinations of torque contributions by the motors, the optimization analysis comprising:
 determining based on the driving cycle information a required shaft speed and torque across all time periods in the driving cycle; 
 calculating, based on the efficiency data, a cost function for the performance objective across all time periods in the driving cycle for each of the potential combinations of torque contributions by the plurality of motors; 
 identifying from the potential combinations of torque contributions one or more combinations of torque contributions that meet the performance objective based on the cost function and that remains within the one or more constraints; and 
 generating, for each time period in the driving cycle, torque command signals for each of the plurality of motors in order to cause the plurality of motors to drive the shaft according to the one or more combinations of torque contributions to meet the performance objective while remaining within the one or more constraints. 
 
 
     
     
       12. The method of  claim 11  wherein the performance objective is meeting a target efficiency value and where the cost function for each of the potential combinations of torque contributions by the motors is the amount of energy used. 
     
     
       13. The method of  claim 12  further comprising estimating for each time period in the driving cycle the energy consumed, and outputting an estimated total energy consumption for the driving cycle. 
     
     
       14. The method of  claim 12  wherein the optimization analysis performed by the controller further comprises integrating an optimization of energy regeneration from braking. 
     
     
       15. The method of  claim 11  wherein the one or more constraints includes the temperature for each motor. 
     
     
       16. The method of  claim 11  wherein the optimization analysis further comprises, for each time period in the driving cycle, calculating the efficiency of each motor in the plurality of motors at the next period in the driving cycle based on the efficiency data and one or more transients. 
     
     
       17. The method of  claim 16  wherein the one or more transients includes thermal transients, and wherein the optimization analysis further comprises calculating thermal transients to determine an estimated temperature for each of the plurality of motors at the end of the next time period. 
     
     
       18. The method of  claim 11  wherein the method is performed by a controller housed within an electric vehicle. 
     
     
       19. The method of  claim 11  wherein the step of generating the driving cycle information is performed using a trip planning tool. 
     
     
       20. The method of  claim 11  wherein the performance objective is maximizing driving range.